1. Field of the Invention
This invention relates generally to a method and apparatus for use in orthopedic surgery, and more particularly, to a method and apparatus for ultrasonic removal of bone cement material during an orthopedic surgical procedure.
2. Discussion of the Related Art
A natural joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace the natural joint with a joint prosthesis. Such joint prostheses include, for example, shoulder, knee and hip joint prostheses. These different prosthetic devices are generally secured by means of bone cement, such as polymethylmethacrylate (PMMA). However, due to any number of reasons, some of the implanted prostheses may require subsequent removal and implantation of a new prosthesis during what is generally referred to as a revision type surgery. As the number of prosthetic implants increases, a corresponding number of revision arthroplasties will also increase.
One of the main challenges facing a surgeon during a revision procedure is the arduous task of complete prosthesis/cement removal. There are various techniques used to remove the prosthesis and bone cement during revision surgery, however, these techniques exhibit disadvantages. For example, manual instruments, such as osteotomes do not offer the surgeon the tactile feedback that aids in distinguishing between the bone cement and the actual bone. High speed burrs or drills have shortened the time required for removal of the bone cement versus the manual instruments. Unfortunately, these types of instruments also lack the tactile feedback which may lead to inadvertent removal or perforation of the patient's cortical bone.
Other techniques used to remove bone cement include the use of ultrasonic mechanical energy. In this regard, electrical energy is converted into mechanical energy, via an ultrasonic transducer. This mechanical energy, in turn, is transmitted through individually tuned tool tips in acoustic waves, causing the tips to vibrate at very high, yet controlled rates of speed. This action breaks down the bone cement in three ways. First, softening by intermolecular friction as the tool tip moves within the cement mantle. Second, by cavitation as the molecular structure begins to rapidly accelerate. Finally, by providing mechanical separation of the cement through cutting, via the tool tip itself. This ultrasonic technique reduces or eliminates some of the previous disadvantages associated with earlier cement removal techniques. However, the ultrasonic technique may further be improved upon.
What is needed then is a method and apparatus for ultrasonic removal of bone cement material which does not suffer from the above mentioned disadvantages and improves upon existing technology. This, in turn, will reduce the incidence of perforation of the cortical bone, reduce the cement removal time, reduce the overall surgical time and therefore, surgical cost, and provide a means for easily removing bone cement which provides a high degree of tactile feedback during the overall surgical procedure. It is, therefore, an object of the present invention to provide such a method and apparatus for ultrasonic removal of bone cement material during an orthopedic surgical procedure.